const num = 1;
num = 999; // Uncaught TypeError: Assignment to constant variable.
const editableObj = { id : 1 }; // {id: 1}
editableObj.id = 999; // {id: 999}
editableObj.name = 'pjh'; // {id: 999, name: 'pjh'}
const nonEditableObj = Object.freeze({ id : 1 }); // {id: 1}
nonEditableObj.id = 999; // {id: 1}
nonEditableObj.name = 'pjh'; // {id: 1}